Shaping and steering optical beams in a compact device with ultra-high resolution and fast speed enables applications in sensing, imaging, ranging, communication, and display. Conventional optical beam steering solutions have been largely based on mechanical mechanisms. For instance, a mechanically rotating mirror is often used in 3D ranging sensors such as commercial lidars [1], and an array of integrated micro-electromechanical system (MEMS) mirrors is used for some projection displays [2]-[4]. Mechanical optical steering solutions are generally slow and susceptible to physical wear and tear as well as vibration. Depending on the realization, these mechanical beam-steering systems may be bulky, consume significant energy, and have a limited steering capability. Furthermore, these mechanical approaches are only capable of steering a light beam, and are incapable of forming arbitrarily shaped light beams as needed for advanced communication, imaging, and sensing applications. Non-mechanical optical beam steering is possible by modifying the effective refractive index of a transmissive (e.g., prism) or reflective (e.g., grating) structure. Liquid crystal spatial light modulators [5]-[7] and acousto-optic spatial light modulators [8] are examples of such commercial systems (e.g., holographic displays).
Monolithic integration of nanophotonic devices and advanced electronic devices on a single chip is bringing up a new opportunity to realize an innovative electro-optic solution towards optical beam forming. Electromagnetic wavefront can be arbitrarily formed by a phased array which consists of spatially separated antennas each with an independent control of phase and amplitude of the signal. The phased array concept has been known for over a century, and was matured primarily during the World War II in the context of electrically-scanned radars. For several decades, radio frequency phased arrays had been used in military applications. Over the past several years, there has been much research and development towards radio frequency phased arrays for commercial applications such as consumer wireless communications and automotive radars [9].
At optical frequencies, electronically controlled solid-state optical phased arrays have been demonstrated since 1990s with limited capability by either heterogeneous or monolithic integration primarily in custom or dedicated fabrication processes [10]-[21].
In a phased array, to create arbitrary electromagnetic beams with high precision, including creating narrow electromagnetic beams per requirement of many applications, over a wide angular range the phased array antenna elements should be placed closely (ideally within half wavelength), the number of antenna elements should be large, and the phase and amplitude of signal at each antenna element should be controllable. Achieving all of these requirements at optical frequencies has been challenging causing the past demonstrations of optical phased arrays to lack the angular resolution (beam width), spatial coverage (unambiguous steering angle), and flexibility to create various beam patterns as needed in many applications. It is one objective of this invention to demonstrate optical phased arrays that allow small antenna spacing, large number of antenna elements, and accurate control of phase and amplitude at each element, simultaneously.
Over the past several decades, motivated by the consumer demand for electronic applications including personal computers and smartphones, the semiconductor foundry processes, in particular silicon and complementary metal oxide semiconductor (CMOS) processes, have witnessed an exponential growth in performance and integration level. In fact, while the performance and functionality of integrated circuits have improved, their cost has remained nearly constant thanks to semiconductor technology scaling. It is one objective of this invention to demonstrate optical phased array architectures that may be realized in commercial foundry semiconductor processes; hence, benefiting from the same benefits that are offered to the electronic integrated circuits. This would be in contrast to traditional approaches where dedicated processes were developed or used for realization of monolithic optical systems. Monolithic realization of optical phased arrays in commercial foundry semiconductor processes enables incorporating electronic control and calibration schemes to assist and improve the performance and robustness of the optical system.
Monolithic optical phased arrays enable commercial applications including lidar (light/laser detection and ranging) such as those that may be used in advanced driver assistance systems (ADAS) and self-driving cars, three-dimensional cameras such as those that may be used in consumer handheld devices and smartphones, and two- and three-dimensional holographic displays. One objective of this invention is to enable low-cost compact realization of optical phased arrays for diverse range of applications including automotive sensors, consumer 3D imagers, sensors, and 2D and 3D displays.